This invention relates to charge transfer imaging and more particularly to a cartridge mounting for locating a cartridge for creating a latent image in a printer adjacent a dielectric surface for receiving the image. The invention has particular application in the location of a cartridge in a printer adjacent a dielectric coated print drum for receiving an image from the cartridge.
The present invention is described herein with reference to an exemplary printer which utilizes a print drum. It will be clear to those skilled in the art that the present invention may also be used in combination with printers utilizing different configurations of image receiving surfaces.
There is an increasing need for peripheral which can accept a computer or word processor output and convert the output to an image on paper, commonly called a "hard copy". Typically such a peripheral is a printer which uses a charge transfer process similar to that described in U.S. Pat. Nos. 4,155,093 to Fotland and Carrish, or 4,160,257 to Carrish, which utilizes a combination of electrodes which can be controlled to place a charge on a drum coated for instance with alumumium oxide impregnated with a wax. In this way latent images are built up corresponding to the image to be produced on the paper and this image is then toned and transferred to the paper and fused. Should it be necessary to produce a second copy, the procedure is repeated to give as many copies as necessary. Further, it is possible to vary the image by electronic control so that parts of the image can be printed, or the complete image can be turned through 90.degree. with respect to the paper. These possible variations make such printers desirable equipment where hard copies of information are required.
The print cartridge is located adjacent the print drum surface and normally extends substantially parallel to the axis of rotation of the drum. The inner surface of the cartridge, which faces the drum surface and includes the source of the charges, must be accurately spaced from the drum such that it is close enough to produce a clear image, and far enough away to prevent flashover between the electrodes of the cartridge and the drum.
An example of cartridge construction is described in applicant's U.S. Pat. No. 4,679,060. This cartridge includes a number of relatively thin planar structural layers. An image is produced by a combination of electrodes at an inner surface of the cartridge, and outer surfaces facing away from the drum are provided with contacts for electrical connection of the electrodes with corresponding spring biased contacts linked to a cartridge control board, also known as a mother board, for controlling the image generation. A suitable configuration of printer for receiving such a cartridge is described in applicant's U.S. Pat. No. 4,516,847. The cartridge also includes an aluminum spine which rigidifies the cartridge and extends outwardly to provide a handle to be used when the cartridge is being fitted or removed from the printer.
The cartridge is mounted in a printer on mounting blocks which are adjusted relative to rigid parts of the print structure using shims to give the desired spacing between the cartridge and the drum surface (typically 0.01 inches). Understandably, it would be difficult to adjust this spacing each time a cartridge was replaced. Accordingly, the mounting blocks are set-up during assembly of the printer and are not normally adjusted during the life of the printer, so that replacement cartridges must be accurately located on the mounting blocks. To achieve this accurate location, the lower contact surface of each cartridge must be accurately sized and therefore formed of a high grade material, typically FR4 fibre glass reinforced epoxy, which adds considerably to the cost of the cartridge. There is also the problem of particles of dust or the like finding their way between contact surfaces of the cartridge and mounting and thus affecting the spacing.
Connections between the contacts on the outer face of the cartridge and the mother board are made by pogo stick type spring contact which depend from the mother board. These contacts are relatively expensive and the total cost of the 260 or so contacts required for a cartridge adds significantly to the total cost of the printer. Also, the spring forces exerted on the cartridge contacts further complicate the accurate location of the cartridge as the forces, though small, tend to push the cartridge towards the drum, and could affect the spacing between the cartridge and drum.
Other forms of cartridges are available which provide the cartridge contacts on the inner face of the cartridge and do not require such expensive spring contacts. However, the mother board contacts for such cartridges must be located in the restricted space between the cartridge and the drum, the space becoming more restricted as larger diameter print drums are utilized. These cartridges also suffer from the disadvantage that the spring forces from the mother board contacts tend to push the cartridge away from the drum, and again could affect the spacing between the cartridge and the drum.
In addition, the above described construction of a cartridge does not facilitate cooling of the cartridge which is desirable to minimize distortion of the cartridge and to minimize undesirable temperature effects which affect the operation of the cartridge.